High vacuum



July 21, 1964 A. A. LANDFORS HIGH VACUUM Filed Feb. 17, 1961 United States Patent 3,141,606 EHGH VACUUM Arthur A. Landfors, Sharon, Mass., assignor to National Research Corporation, Cambridge, Mass, a corporation of Massachusetts Filed Feb. 17, 1961, Ser. No. 89381 9 Claims. (Cl. 230-101) This invention relates to a high vacuum device and more particularly to an improved high vacuum diffusion pump.

A principal object of the present invention is to provide an improved diffusion pump which is rugged in construction and inexpensive to manufacture.

Another object of the invention is to provide a diffusion pump of the above type which can be readily assembled and disassembled with accurate position of the parts thereof for optimum operating conditions.

Still another object of the invention is to provide a diffusion pump of the above type having minimum backstreaming while still providing high pumping speeds and a high forepressure tolerance.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein there is shown a diagrammatic sectional view of a preferred embodiment of the present invention.

Generally, the invention is directed to an improved high vacuum diffusion pump having excellent forepressure tolerance with high pumping speeds through a wide range of pressures. The pump is designed so that it can be readily assembled and disassembled to give ease of manufacture and maintenance. The pump includes a generally cylindrical pump body of conventional design with a vapor jet assembly positioned inside of the cylindrical pump body, the jet assembly being smaller than the pump body and defining the pumping chamber with the pump body. The jet assembly preferably includes a plurality of jets designed to discharge jets of diffusion pump oil vapors downwardly into the pumping chamber. A boiler is provided for vaporizing diffusion pump oil at the bottom of the pump body, these vapors passing upwardly through the jet assembly and outwardly and downwardly through the jets. The foreline is connected to the pump body adjacent the bottom of the pumping chamber and forms an ejector stage having a high forepressure tolerance.

The jet assembly is preferably formed of a number of superposed separate sections which are built up, one on top of the other, to form the whole assembly, these being preferably held together by a single fastening means. These superposed individual sections have cooperating skirt and shoulder portions which together define the various jets, as more fully described hereinafter. The boiler, comprising a heater and a boiler section of the pump, is arranged to provide very high heat input to give high pumping speeds while still preventing backstreaming of oil vapors or the blowing of oil back up the pump body.

Referring now to the drawing, there is illustrated at it a generally cylindrical pump body having therewithin a jet assembly which is generally indicated at 12. The pumping space between the jet assembly and the interior of the cylindrical pump body is shown at 16. The pump body is provided with a foreline 18 having a straight section 3,1415% Patented July 21, 1964 "ice 2i? and a diffuser section 38 formed integrally therewith.

The oil level is indicated by a wavy line in the boiler section 22 at the bottom of the pump. The bottom of this boiler section is defined by a heat transfer element 24 which is shown as having heating fins 25 extending upwardly into the oil. A heating element 26 is provided in thermal contact with the peripheral portion of the boiler section bottom 24.

The jet assembly 12 includes, in the illustrated embodiment, three downwardly directed jets 3t 32 and 34 and an ejector stage jet 36. The top jet 3t) is fed by a vapor tube 31 extending from adjacent the bottom of the boiler section to the top of the jet assembly.

Cooling coils 40 are provided around portions of the pump body and the foreline and a separate cooling coil 42 is provided at the bottom of the boiler section immediately adjacent the outer periphery of the pump body so as to provide cooling adjacent the oil return passage to the boiler section when desired.

The jet assembly is made up of a number of superposed portions, the bottom section having a main body portion shown at St? with an inwardly tapered shoulder 52, upwardly extending cylindrical portion 58, and another inwardly tapered shoulder portion 54. The next section includes a skirt portion 69, a cylindrical portion 61, an inwardly extending shoulder portion 62 and a top cylindrical section 63. As can be seen, the shoulder portion 52 of the bottom section and the skirt portion 60 of the next upper section of the jet assembly define a space 71) which terminates in the vapor jet 34. The inner portion of this space 7% is larger in area than is the converging throat of the jet. The space 7t? is provided with pumping vapors through holes '72 which communicate with the interior of the jet assembly. This arrangement provides for an even distribution of the vapors into the narrowest portion of the jet 34 so as to provide optimum pumping action around the whole periphery of the jet.

The next upper jet is formed in a similar fashion by cooperation of skirt portion 66 and shoulder portion 62 which provide a vapor space 74 which is fed by vapors coming through holes 76. The top jet is formed in a conventional fashion by providing a downwardly projecting skirt 68 which is fed by pumping vapors passing through holes 78. A rod is connected between the top of the jet assembly and the boiler section bottom 24 to prevent separation of the superposed sections constituting the whole jet assembly 12. In assembling the pump, the superposed sections are placed on top of each other, the various elements being accurately spaced by the cooperating shoulder and skirt portions, and are then fastened securely by means of the rod '80.

As illustrated, the ejector tube 36 provides a strong blast of oil vapors into the diffuser section 38 of the foreline so as to increase the forepressure tolerance of the diffusion pump. As mentioned previously, it is quite important to prevent excess heating of the oil immediately adjacent the periphery of the pump body. If this is not done, violent boiling at the bottom of the section will actually throw particles of oil upwardly along the outer wall of the pump body, giving a very serious backstreaming effect when maximum power is being put into the boiler. However, the recess in the boiler section bottom 24 adjacent the cooling coil 42 reduces the heat flow to the edge of the pump and thus maintains the oil flowing back to the boiler section in a cooled condition.

Another feature of the pump of considerable importance is the cutaway portion 27 of the heater which limits somewhat the effectiveness of heat transfer between the heater 26 and the boiler section bottom 24. This gives the proper distribution of oil vapors, particularly at very high heat input. However, the chief purpose of the recess 27 is to reduce the temperature at the center of the boiler, section thereby preventing oil breakdown.

Other features of the pump, such as the fastening flanges and the rings (illustrated at 82), are conventional and need not be discussed in detail.

While the invention has been described in connection with a preferred embodiment thereof, it should be apparent that numerous alternative arrangements can be provided without departing from the spirit of the invention.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative, and not in a limiting sense' What is claimed is:

1. A high vacuum diffusion pump comprising a pump body, a vapor jet assembly positioned within said pump body, said jet assembly being smaller than said pump body and defining a pumping chamber with said pump body, at least one jet forming means, located at the top of said jet assembly, arranged to discharge a jet of diffusion pump oil vapors downwardly into said pumping chamber and at least one additional jet forming means, located at a central portion on said jet assembly, arranged to discharge a jet of diffusion jump oil vapors downwardly into said pumping chamber, a boiler for vaporizing diffusion pump oil at the bottom of said pump body, the bottom of said jet assembly being open to vapors generated in said boiler, a foreline connected to said body adjacent the bottom of said pumping chamber, at least one of said additional jet forming means comprising upper and lower outwardly flared portions defining a vapor space which communicates with the interior of the jet assembly by restricted openings, said upper and lower flared portions converging as they extend outwardly from the axis of the jet assembly to form a converging nozzle throat and then diverging to form a diverging downwardly directed nozzle.

2. A high vacuum diffusion pump comprising a pump body, a vapor jet assembly positioned within said pump body, said jet assembly being smaller than said pump body and defining a pumping chamber with said pump body, at least one jet on said jet assembly arranged to discharge a jet of diffusion pump oil vapors downwardly into said pumping chamber, a boiler for vaporizing diffusion pump oil at the bottom of said pump body, the bottom of said jet assembly being open to vapors generated in said boiler, 21 foreline connected to said pump body adjacent the bottom of said pumping chamber, said jet assembly being formed of superposed sections having flared skirt portions, generally cylindrical portions and in wardly projecting shoulder portions, the shoulder of a lower section cooperating with the skirt of the next upper section to form a vapor jet having a vapor space which communicates with the interior of the jet assembly by restricted openings, and cooperating shoulder and skirt converging as they extend outwardly from the axis of the jet assembly to form a converging nozzle throat and then diverging to form a diverging downwardly directed nozzle.

3. A high vacuum diffusion pump comprising a pump body, a vapor jet assembly positioned within said pump body, said jet assembly being smaller than said pump body and defining a pumping chamber with said pump body, at least one jet on said jet assembly arranged to discharge a jet of diffusion pump oil vapors downwardly into said pumping chamber, a boiler for vaporizing dif fusion pump oil at the bottom of said pump body, the boiler comprising a boiler section of the pump body and a heater in heat transfer contact with said boiler section of the pump body, the bottom of said jet assembly being open to vapors generated in said boiler, a foreline connected to said pump body adjacent the bottom of said pumping chamber, means for cooling the pump, gen erally cylindrical portions and inwardly projecting shoulder portions, a top jet on said jet assembly, means defining a separate vapor passage leading from the boiler section of the pump body to the top jet, and means formed in said boiler for reducing the heat input to the portion of the boiler supplying vapors to the top jet.

4. The pump of claim 1 comprising an ejector in fluid communication with the vapor jet assembly for discharging vapor from the interior of the jet assembly into the said foreline, the foreline comprising a vertical section and a horizontal section connecting the vertical section to the pump body, means for circulating a cooling fluid in heat transfer relation with the vertical section, a substantial length of the horizontal section being free of cooling means.

5. In a high vacuum diffusion pump comprising a vertically arranged pump body, means for cooling said pump body, a vapor jet assembly positioned within said pump body, said vapor jet assembly being smaller than said pump body to define therewith a pumping chamber, said vapor jet assembly being constructed and arranged to discharge jets of diffusion pump fluid vapors downwar ly and outwardly from said vapor jet assembly into said pumping chamber, a boiler for vaporizing diffusion pump fluid at the bottom of said pump body, the bottom of said vapor jet assembly being open to vapors generated in said boiler, a foreline connected to said pump body adjacent the bottom of said pumping chamber,

(a) said jet assembly comprising a vertical series of stacked sections,

(b) fastening means restraining the stacked sections from vertical movement so that the pressure of vapors generated in said boiler does not force the sections to move upwardly,

(c) the stacked sections including a pair of adjacent upper and lower sections,

(d) the lower one of said adjacent sections comprising upper and lower inwardly bent shoulder portions and a transition section of generally cylindrical form therebetween,

(e) the upper one of said adjacent sections comprising at least one generally cylindrical portion, a skirt portion flaring outwardly from one of said cylindrical portions and a shoulder portion bent inwardly from one of said cylindrical portions,

(f) one of said inwardly bent portions of the upper section resting on the upper inwardly bent shoulder portion of the lower section to vertically align the two sections,

(g) the upper section being constructed so that its said skirt is spaced above the lower shoulder portion of the lower section to define a space therewith, and

(h) passage means placing the interior of the vapor jet assembly in communication with the space.

6. The diffusion pump vapor jet assembly of claim 5 wherein each of said adjacent sections is a single sheet metal tube, the said passage means comprising orifices in said lower tube in the said transition portion thereof.

7. In a high vacuum diffusion pump comprising a vertically arranged tubular pump body, means for cooling the pump body, a vapor jet assembly positioned within said pump body, said jet assembly being smaller than said pump body and defining a pump chamber with said pump body, at least one nozzle on said jet assembly arranged to discharge a jet of pump oil vapors downwardly into said pumping chamber, a boiler for vaporizing diffusion pump oil at the bottom of said pump body, the bottom of said vapor jet assembly being open to vapors generated in said boiler, a foreline connected to said pump body adjacent the bottom of the pumping chamber,

(a) means defining an oil return passage for condensed oil traveling to the boiler from the pumping chamber, said passage including the bottom of the pumping chamber,

(b) the boiler comprising a heat transfer element covering the lower end of the tubular pump body and con- 5 ducting heat to the pump oil within the oil return passage and Within the interior of the vapor jet assembly,

(c) the improvement comprising: means formed in said boiler for reducing heat transfer through said element to the collected pump oil in the oil return passage so that premature reboiling of the collected pump oil at the lower end of the pumping chamber is prevented.

8. The pump of claim 7 wherein the means formed in said boiler for reducing heat transfer comprises a portion of said heat transfer element of reduced thickness adjacent the oil return passage.

6 9. The pump of claim 8, wherein the portion of reduced thickness comprises a recess in said element facing outwardly from the pump, the pump further comprising a cooling coil located in said recess.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,021 Alexander et al July 16, 1946 2,797,043 Gerow June 25, 1957 2,886,235 Denton May 12, 1959 2,933,233 Gerow et a1. Apr. 19, 1960 FOREIGN PATENTS 513,560 Canada June 7, 1955 UNITED STATES PATENT oFrIcE CERTIFICATE OF CORRECTION Patent No, 3 l4l 606 July 21, 1964 Arthur A, Landfors It is hereby certified that error appears in the above numberejfd patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 27 for "jump" read pump line 31 before "body" insert pump line 56 for "and" first occurrence read said same column 3 lines 74 and 75 and column 4 line 1 strike out generally cylindrical portions and inwardly projecting shoulder portions" and insert instead body -v Signed and sealed this 19th day of January 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A HIGH VACUUM DIFFUSION PUMP COMPRISING A PUMP BODY, A VAPOR JET ASSEMBLY POSITIONED WITHIN SAID PUMP BODY, A SAID JET ASSEMBLY BEING SMALLER THAN SAID PUMP BODY AND DEFINING A PUMPING CHAMBER WITH SAID PUMP BODY, AT LEAST ONE JET FORMING MEANS, LOCATED AT THE TOP OF SAID JET ASSEMBLY, ARRANGED TO DISCHARGE A JET OF DIFFUSION PUMP OIL VAPORS DOWNWARDLY INTO SAID PUMPING CHAMBER AND AT LEAST ONE ADDITIONAL JET FORMING MEANS, LOCATED AT A CENTRAL PORTION ON SAID JET ASSEMBLY, ARRANGED TO DISCHARGE A JET OF DIFFUSION JUMP OIL VAPORS DOWNWARDLY INTO SAID PUMPING CHAMBER, A BOILER FOR VAPORIZING DIFFUSION PUMP OIL AT THE BOTTOM OF SAID PUMP BODY, THE BOTTOM OF SAID JET ASSEMBLY BEING OPEN TO VAPORS GENERATED IN SAID BOILER, A FORELINE CONNECTED TO SAID BODY ADJACENT THE BOTTOM OF SAID PUMPING CHAMBER, AT LEAST ONE OF SAID ADDITIONAL JET FORMING MEANS COMPRISING UPPER AND LOWER OUTWARDLY FLARED PORTIONS DEFINING A VAPOR SPACE WHICH COMMUNICATES WITH THE INTERIOR OF THE JET ASSEMBLY BY RESTRICTED OPENINGS, SAID UPPER AND LOWER FLARED PORTIONS CONVERGING AS THEY EXTEND OUTWARDLY FROM THE AXIS OF THE JET ASSEMBLY TO FORM A CONVERGING NOZZLE THROAT AND THEN DIVERGING TO FORM A DIVERGING DOWNWARDLY DIRECTED NOZZLE. 